This invention relates generally to building ventilation systems. More particularly, the present invention relates to building ventilation systems having apparatus for recovering the heat in the air exhausted from the ventilated area.
Ventilating systems are commonly used to maintain indoor environmental standards in industrial buildings, commercial office buildings, schools and farming facilities. Such buildings include foundries, factories, metal finishing areas, work shops, service areas, warehouses, meeting halls, recreational buildings, animal nursery and feeder houses, swimming pools and other facilities of many diverse types. Ventilation systems for such facilities are necessary to remove excess heat, discharge pollutants and unwanted moisture and to maintain a healthful, comfortable environment. Unfortunately, safety, health and economic considerations are at odds with one another in that air, which has been heated or cooled at substantial expense, is virtually thrown away by the conventional ventilation process.
In the case of a heated facility, the exhaust air of the ventilation process contains not only the sensible energy expended in increasing the supply air temperature but the latent energy represented by the vaporized water required to adequately humidify. With great pressure on power-producing utilities and the ever-increasing cost of fuels for heating and cooling, there is a great need to recover thermal energy from the exhaust air of all high performance ventilation systems.
Conventional ventilation thermal energy recovery systems have used rotating wheel heat exchangers as well as non-rotating cross-flow heat exchangers. Heat exchangers of these types have been constructed from metals such as stainless steel and aluminum and from certain ceramics such as aluminum oxide and silicon carbide. Such materials, while structurally sound, are expensive and have little or no capability of storing and releasing moisture not to mention the high maintenance required and lack of ability to provide free cooling when energy is not required to be recovered.